This invention relates to an improved tubesheet composition and method of forming the tubesheet. In one particular embodiment, an improved method of preparing a dry cellulose ester hollow fiber membrane device is disclosed.
A variety of techniques for drying water-wet cellulose ester membranes are known in the prior art. It is essential that the drying be conducted in a manner which does not deleteriously affect the pore structure and consequently the membrane characteristics of the hollow fiber. U.S. Pat. No. 4,430,807 and a number of references cited therein describe the displacement of water from cellulose ester membranes using organic solvents. U.S. Pat. No. 4,127,625 describes the treatment of the membrane with a salt solution followed by freeze drying.
It has been found convenient to assemble water-wet, cellulose ester hollow fiber membranes into a bundle complete with one or more tubesheets and then to dry the bundle. U.S. Pat. Nos. 3,228,876, 3,422,008, 3,455,460 and 3,755,034 are illustrative of some of the methods described in the art for fabrication of hollow fiber membranes devices. Techniques for the formation of tubesheets on hollow fiber membrane devices are also disclosed in U.S. Pat. Nos. 3,339,341, 3,423,491, 3,619,459, 3,722,695, 3,728,425 and 4,138,460. U.S. Pat. No. 4,323,454 suggests at column 4, lines 19-31 that a tubesheet can be cast in successive castings.
Cellulose ester hollow fiber membranes shrink significantly in cross-section upon drying. It has now been discovered that this shrinkage can produce unrelieved tensions, distortions, delaminations and cracks in the tubesheet. A convenient method of repairing the tubesheet is desirable.